The present invention relates generally to household appliance control systems and associated sensors and in particular to pressure sensors for detecting pressure oscillations in the cleansing liquid used in an appliance such as a dishwasher or clothes washing machine.
One approach to energy use reduction in household appliances such as clothes washers and dishwashers is to optimize the use of water and the time of various cleansing cycles so that effective cleansing is accomplished while minimizing excess time or water used in the process. Commonly these types of household appliances use open loop control systems in which the cleansing liquid (typically water) is introduced into the machine for a predetermined period of time and the machine then operates through various cycles (such as washing, rinsing, and spinning in a clothes washer or washing, rinsing, and drying in a dishwasher) for predetermined periods of time. Such systems of necessity are designed to provide adequate cleaning in worst-case scenarios of large loads of heavily soiled articles; this arrangement frequently involves the use of more cleansing liquid and longer operating cycles than might be required to adequately clean the items in the machine.
One approach to minimizing energy consumption in such appliances has been the incorporation of closed loop control systems in which feedback from sensor measuring selected operating parameters of the machine are used to control operating cycles of the machine. For example, pressure sensors can be used in a wet appliance (that is, an appliance using a cleansing liquid) to generate signals corresponding to pump output pressure and that can be used in such a feedback system to optimize appliance operation. One example of such a control system in disclosed in U.S. Pat. No. 5,313,964, entitled "Fluid-Handling Machine Incorporating a Closed Loop System for Controlling Liquid Load," which is assigned to the assignee herein and incorporated herein by reference.
Pressure sensors of the type suitable for use in a closed feedback control system in household appliances are desirably simple in construction, rugged, long-lasting, and inexpensive to manufacture and install. Further, such pressure sensors typically need to be responsive at relatively low pressures (e.g., pressures of 15 pounds (pounds per square inch differential--psid) or less). Solid state silicon type pressure sensors can provide electrical signals over the low pressure ranges of interest in household appliance operation; such sensors, however, can degrade in the adverse operating environment (e.g., dampness and chemicals commonly used in detergents, such as phosphates, chorine, and the like) to which the household appliance is commonly exposed and further have a cost that effectively makes their use prohibitive in common household appliances.
A need thus exists for a simple, rugged, and inexpensive pressure sensor device that can be incorporated into a closed feedback control system used to improve energy efficiency of household appliances.